Technical Abstract:
The ability to simulate the effects of nitrogen on leaf growth and canopy development is important for potato simulation models that can be used to manage nitrogen applications. Most models simulate the effects of nitrogen on canopy growth at the whole plant level, i.e., the plant is viewed as a "big leaf". Recently, more mechanistic, leaf level models of photosynthesis have been developed to better estimate carbon assimilation and evapotranspiration rates as a function of environmental and basic physiological variables. In order to scale the simulations to the whole plant level, information on the growth of individual leaves is necessary. The relationship between carbon assimilation and N uptake is further complicated by atmospheric CO2 concentrations and the effects on carbon assimilation rate, carbon partitioning and N content in the plant. The objective of this study was to quantify leaf expansion rates in potato as a function of nitrogen application rate and CO2 level. Data on leaf growth rates were obtained from an experiment with potato carried out in pots in outdoor daylit growth chambers. Six N levels (2 to 14 mM N) and two CO2 levels (ambient and twice ambient) were applied with irrigation. A day/night temperature regime of 23/18 oC was maintained. Length and width were measured two times a week on selected mainstem and apical leaves. A Gompertz type equation was used to smooth the leaf area data. Leaf growth rates were calculated from the change in area over time and relative leaf age (Fleisher and Timlin, 2006). An empirical function was determined from the data to calculate the effect of N level on maximum leaf expansion rate The conclusions from this study are 1) the rate of expansion of a leaf and its final area are functions of nitrogen availability but the growth duration is not, and 2) carbon limitations also affect leaf expansion rates, especially for higher order leaves in potato. A function for leaf expansion rate that accounts for leaf age effects on growth rate with temperature and nitrogen adjustments appears to be a promising method to simulate leaf expansion in potato.